Depth was very important because the push back was used to destroy the enemy formation. Athenians used a base level of 8 deep, Spartans 12, Thebans 25 and the Macedonians up to nearly 50 in some situations (although 16 was normal and 32 "double depth.") These larger units were being used like human battering rams to destroy other hoplite phalanx units. The formations were already dense, so adding that much depth would have been made them into a streamroller. I really don't understand what kept the men in the first ranks from being crushed...unless of course, their opponent was pushed back.

The observation about MTW was on the money. If you used thin lines, they became weak after a few casualties. As a result each of us learned to use depths that provided an optimum of hitting power and durabitily (depending on play style and situation.)

I'm sure I'm still missing alot on the intricacies of ancient warfare but this is what I'm gathering at the moment: phalanx formations were typically quite large in full size armies: around 2 to 4,000 per wing was not uncommon although they did have smaller divisions within of 256 men, 1000, etc. They didn't have to operate as a block per wing, but it appears that they often did. A phalanx wing of 4,000 was more men than the entire hastati/principes/triarii of a single legion. It's an intersting comparison when you think about it. The Roman system is similarly deep...but in multiple lines, whereas the phalanx is a compact single line.

To make something like this in RTW you need to have individual phalanx components sort of welded together, but still breakable at the joints. The Romans exploited any breaks in the formation, so you still want phalangite sub units do be prone to getting disordered, taking too many casualties etc. However, the AI and the human need to be able to wield the phalangites more like a line. It's a tough balancing act: a hard, but brittle phalanx.

On the other hand, you can also see where the Roman system should work against the phalanx. The phalanx can't afford to push forward (or fall back) too much in any sectio or it creates a vulnerable gap, one the Roman infantry was designed to very effectively exploit. The phalangites also are prone to being disordered by any obstacles in their path or breaks in the terrain. So during melee, the phalangites are all stuck in their deep formation unable to rotate to rest. Meanwhile the Romans can attack in thin waves keeping a steady pressure, with the previous wave falling back to catch their breath (since their formations did not need to be rigid and deep.) It would be interesting to see how this drill was carried out.

The high kill rates of RTW (or any TW game) cause problems with the idea though. You can't effectively disengage sword infantry, and they take a lot of casualties fighting so they nearly always fight to the death. So you can't really pull back your hastati in sections, then advance princeps, etc. as the Romans apparently did. It would look kind of dull waiting for the phalangites to wear down and become disordered while your hastati get pushed back, then replaced by princeps, then perhaps hastati again, etc. until the phalanx wore down or became disordered or caused enough damage to your legion (or legion's position) to win.